Likewise, the seller of call options is obligated to sell stock at a certain price by a certain date if the buyer chooses to exercise his right. (borntosell.com)
If you increase the price of an ebook, you may make more money at a certain price point, even if you sell fewer ebooks. (justwriteabook.com)
They typically act as liquidity providers, standing ready to buy and sell at certain price levels. (bloomberg.com)